The Hemolytic Uremic Syndrome [HUS] Italian Registry System, in cooperation with the National Institute of Health (Istituto Superiore di Sanita ISS], http://www.iss.it/seu) and the Italian Society for Pediatric Kidney Diseases (SINP), has been informed about several reported cases of HUS in patients resident in the region of Apulia [Puglia] or in people who traveled there before the onset of symptoms.

Between 1 and 14 Aug 2013, 8 children and an adult patient were hospitalized after developing HUS. Most HUS cases are secondary to a Shiga toxin-producing _Escherichia coli_ infection (also called an enterohemorrhagic _E. coli_ or EHEC), with diarrhea, often with bloody stool, vomiting, and abdominal pain. Preliminary laboratory investigations performed by the National Reference Laboratory for _E. coli_ at ISS on 2 patients revealed an infection with EHEC O26. Further investigation on the other cases is ongoing.

The Apulia Region Health Authorities are conducting epidemiological investigations with Ministry of Health and the ISS. These activities have not been able so far to ascertain with certainty a common source of infection. Regional authorities are enhancing their epidemiological surveillance on local gastroenteritis activity, while the ISS sent an alert message to all Italian pediatric kidney diseases departments, through the SNIP, for early detection of other cases in the various regions, possibly linked to the Apulia outbreak. For the same reason, ISS sent an alert message to the European Center for Disease Prevention and Control (ECDC).

In a 2-week period, 9 cases of hemolytic uremic syndrome have been diagnosed in Puglia in south eastern Italy. Usually, HUS occurs in no more than 5-10 per cent of cases, suggesting that as many as 200 cases of the infection could have occurred. ProMED-mail awaits more information regarding this Italian outbreak.

In analyzing the genetic and phenotypic profiles of non-O157 groups, it has been found that they belong to their own lineages and have unique profiles of virulence traits different from O157 (1). The serogroups appearing to be most prominent are O26, O111, O128, and O103 (2), the former serotype being the implicated strain in this outbreak.

If a laboratory is using sorbitol-MacConkey (sMAC) plates to identify VTEC by virtue of O157's inability to ferment sorbitol, the non-O157 strains will be missed. In a 3-year pediatric study from the University of Washington, USA (3), 1851 stool samples were processed for sorbitol fermentation as well as toxin production by EIA (enzyme immunoassay), and 28 strains of O157 were found along with O103 (4 strains), O118 (2 strains), O111 (2 strains), and 3 other strains.

Clinically, the O157 infections had a higher frequency of bloody stools, fecal leukocytes, and abdominal pain with shorter symptom duration. Five (18 per cent) of O157 infections developed hemolytic uremic syndrome (HUS); none of the non-O157 strains did. Since toxin assay did not identify all O157 strains found on sMAC plates, the investigators did not advocate performing toxin assay alone. Non-O157 can produce HUS, as demonstrated by a cluster of O121 cases associated with a lake in Connecticut, USA (4).

Since toxin assays are not uniformly performed in many areas, and most cases do not produce HUS, it is likely that cases due to non-O157 strains are being missed. How frequent this phenomenon will become over time is unclear.